This invention relates generally to lifts for boats, and more particularly to a lift that uses a hydraulic cylinder such that a ram of the cylinder retracts into the cylinder to move the lift into a raised storage position.
Devices for lifting boats out of water for storage are well known. One common design utilizes a frame that has a base which is rectangular in outline when viewed from above. Booms are pivotally attached to the base and are connected at their tops by a boat rack. The booms, the boat rack, and the base form a parallelogram when viewed from the side. The booms pivot from a position wherein the boat rack is below the water level for loading and unloading a boat, to a raised storage position wherein the boat is held above the water level. Typically a hydraulic cylinder is connected diagonally across the parallelogram between the booms and the base. As the ram of the cylinder extends, the boat rack is raised towards the storage position. As the ram of the cylinder retracts, the boat rack is lowered. An example of this design is shown in U.S. Pat. No. 3,021,965.
In the traditional design some type of locking mechanism is generally required to hold the lift in the raised position. If these locking mechanisms fail, unexpected lowering of the boat or excessive stress on the hydraulic cylinder can occur. Furthermore the locks add to the mechanical complexity and inconvenience of the lifts. A solution to these problems has been proposed in U.S. Pat. No. 4,895,479 which suggests pivoting the booms over center to a raised storage position in which the weight of the boat helps hold the lift in the storage position. This solution has effectively eliminated many of the problems of prior art lifts.
However, all the aforementioned lifts have the disadvantage of having the ram of the hydraulic cylinder extended during storage. The primary disadvantage of this arrangement is that the ram is exposed when the lift is in a raised storage position. Because most lifts are in the raised storage position the majority of the time, this means the ram is exposed the majority of the time. Exposure of the ram to the water for extended periods of time allows fouling of the ram by the growth of algae, moss, barnacles, and similar aquatic life. The possibility of rusting and corrosion of the rod are also increased by exposure to water and elements present in the water.
The difficulties encountered in the prior art and discussed above are substantially eliminated by the present invention.